The focus of this project is the development of appropriate statistical methodologies for analysis of genotoxicity data from a variety of animal and microbial systems. Investigations continued into the statistical analysis of data on aneuploidy induction (chromosomal loss or gain) in yeast. Statistical methods were constructed using parametric models that incorporate the unique downturn in dose-response seen in aneuploidy experimentation. Application to recently-published data showed a greater sensitivity of the new methods to correctly identify aneuploidy induction than that seen with previous methods. Investigations were also begun into the modeling and analysis of data from developmental toxicity experiments, with specific attention directed at the dominant lethal assay in the male mouse. Of interest is identification of possible overdispersion induced by treating paternal units and then sampling progeny from such experiments. Statistical methods for addressing such data were considered that require minimal assumptions on the distribution of the response; these include bootstrapping and rank-based analyses.